Methylcitrate synthase from Aspergillus fumigatus -: Propionyl-CoA affects polyketide synthesis, growth and morphology of conidia
Methylcitrate synthase from Aspergillus fumigatus -: Propionyl-CoA affects polyketide synthesis, growth and morphology of conidia
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DOI：
10.1111/j.1742-4658.2005.04784.x
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发表时间：
2005-07-01
期刊：
影响因子：
5.4
通讯作者：
Brock, M
中科院分区：
文献类型：
--
作者：
Maerker, C;Rohde, M;Brock, M
柠檬酸甲酯合成酶是柠檬酸甲酯循环的关键酶，是真菌降解丙酸的必需酶。丙酸盐不仅作为碳源，而且作为食品防腐剂（E280-283），对聚酮化合物的合成具有负面影响。为了研究人类机会致病真菌烟曲霉的丙酸代谢，对甲基柠檬酸合酶进行了纯化和表征。纯化的酶显示柠檬酸和甲基柠檬酸合酶活性，并显示出类似的特性，从构巢曲霉相应的酶。A.对烟曲霉酶进行了鉴定，并构建了缺失菌株用于表型分析。缺失导致不能在丙酸盐作为唯一碳源上生长。在含有葡萄糖和丙酸盐的培养基上观察到生长速率和孢子颜色形成的强烈降低，这与丙酰辅酶A的积累一致。类似地，使用缬氨酸、异亮氨酸和甲硫氨酸作为氮源，其在降解时产生丙酰辅酶A，抑制生长和聚酮化合物产生。这些作用是由于丙酮酸脱氢酶复合物的直接抑制和丙酰辅酶A对聚酮合成的阻断。分生孢子表面进行了研究，通过电子扫描显微镜和揭示孢子颜色和分生孢子表面的平行度之间的相关性。此外，当在昆虫感染模型中测试时，甲基柠檬酸合酶缺失导致毒力减弱，并且当应用来自葡萄糖/丙酸盐培养基的发白分生孢子时，毒力减弱甚至更明显。因此，甲基柠檬酸合酶在感染过程中的影响进行了讨论。
Methylcitrate synthase is a key enzyme of the methylcitrate cycle and required for fungal propionate degradation. Propionate not only serves as a carbon source, but also acts as a food preservative (E280-283) and possesses a negative effect on polyketide synthesis. To investigate propionate metabolism from the opportunistic human pathogenic fungus Aspergillus fumigatus, methylcitrate synthase was purified to homogeneity and characterized. The purified enzyme displayed both, citrate and methylcitrate synthase activity and showed similar characteristics to the corresponding enzyme from Aspergillus nidulans. The coding region of the A. fumigatus enzyme was identified and a deletion strain was constructed for phenotypic analysis. The deletion resulted in an inability to grow on propionate as the sole carbon source. A strong reduction of growth rate and spore colour formation on media containing both, glucose and propionate was observed, which was coincident with an accumulation of propionyl-CoA. Similarly, the use of valine, isoleucine and methionine as nitrogen sources, which yield propionyl-CoA upon degradation, inhibited growth and polyketide production. These effects are due to a direct inhibition of the pyruvate dehydrogenase complex and blockage of polyketide synthesis by propionyl-CoA. The surface of conidia was studied by electron scanning microscopy and revealed a correlation between spore colour and ornamentation of the conidial surface. In addition, a methylcitrate synthase deletion led to an attenuation of virulence, when tested in an insect infection model and attenuation was even more pronounced, when whitish conidia from glucose/propionate medium were applied. Therefore, an impact of methylcitrate synthase in the infection process is discussed.